The present invention relates to a high-frequency heating apparatus for heating a single object and for simultaneously heating a plurality of objects which have different temperatures at the start of heating or different heat absorbing capacities, and also to a heating method.
Examples of conventional apparatuses of this kind are disclosed in the Unexamined Japanese Patent Application Publication Nos. Hei6-201137 and No. Hei9-27389 and control the heating of objects based on a detection signal from a temperature detection means.
FIGS. 22 and 23 show a combination of a temperature detection means 2 for an object 1 being heated, which is described in the Unexamined Japanese Patent Application Publication No. Hei6-201137, and a mounting table 3. FIG. 22 shows an apparatus which includes amounting table 3 mounted with an object 1 and adapted to be rotated and a temperature detection means 2 for the object 1. An infrared sensor is used for the temperature detection means 2, and the radius segment of the rotatable mounting table 3 is taken as an angle of view. FIG. 23 shows an apparatus in which the infrared sensor is swung by a drive means 4 so that the radius segment of the mounting table 3 defines a view angle. In either case, temperature detection means 2 is situated above a heating chamber 5.
According to the Unexamined Japanese Patent Application Publication No. Hei9-27389, as shown in FIG. 24 and FIG. 25, the apparatus has a plurality of power feed portions 11a, 11b for supplying high frequency electromagnetic wave and alternately switches between these power feed portions to perform concentrated or distributed heating to eliminate temperature variations. This apparatus is intended to heat a single object.
In FIGS. 24 and 25, the apparatus has a temperature detection means 13 for an object 12 being heated, a plurality of power feed portions 11a, 11b for feeding high frequencies to a heating chamber 14, and a distribution change means 15 for changing the positions of the power feed portions 11. There are a plurality of power feed portions 11 and they are alternately switched on to perform concentrated or distributed heating thereby eliminating temperature variations. When the peripheral portion of the object 12 on a rotating table 16 becomes hot, the power feed portion 11a is opened to switch to the concentrated heating of the central part. When the central part of the object 12 on the rotating table 16 becomes hot, the power feed portion 11b is opened to switch to the distributed heating over a wide area.
Further, the same official gazette also discloses another apparatus which, as shown in FIGS. 26 to 28, has a combination of a temperature detection means 18 for an object 17 and amounting table 19 that does not rotate, with an infrared sensor as the temperature detection means 18 arranged to take the entire mounting table 19 as its view angle. The apparatus also includes a shield plate 21 formed with an opening as a power feed portion 20a and a shield plate 22 formed with an opening as a power feed portion 20b. The shield plates 21, 22 are rotated in combination. When the peripheral portion of an object 17 becomes hot, the rotation combination is switched so that the central part of the power feed portion 20a is open. When the central part of the object 17 becomes hot, the rotation combination is switched so that the peripheral part of the power feed portion 20a is open. The power feed portions 20a, 20b are situated immediately below a bottom surface wall of the mounting table 19 and the temperature detection means 18 is situated above a top surface wall of a heating chamber 23.
That is, the apparatus of the Unexamined Japanese Patent Application Publication No. Hei6-201137 uses a combination of the rotating table and the temperature detection means, which takes almost the radius segment of the rotating table as its view angle. The apparatus of the Unexamined Japanese Patent Application Publication No. Hei9-27389 has a plurality of power feed portions for supplying a high-frequency radiation and performs local heating by selecting one of the power feed portions and uniform heating by alternately turning them on. Further, the other apparatus of the Unexamined Japanese Patent Application Publication No. Hei9-27389 combines the non-rotating mounting table 19 with the temperature detection means which takes almost the entire mounting table 19 as the angle of view.
However, the conventional configurations all heat the objects under the same condition (same temperature, same kind and same heat absorbing capacity). Hence, the angle of view of the temperature detection means does not matter much.
When the heating that applies a high frequency radiation to all objects is combined with the heating that high-frequency-heats a particular object concentratedly as in this embodiment, new problems arise in realizing the simultaneous heating of a plurality of objects having different temperatures at the start of heating or different heat absorbing capacities to the same temperature, not possible with the conventional high-frequency heating apparatus.
That is, when a plurality of objects are heated simultaneously, if a temperature difference between the objects being heated is detected, the rotation of the mounting table is stopped so that the lower-temperature object is situated near the power feed portion for concentrated heating by the high-frequency radiation. Hence, the temperature of the object on the mounting table near the power feed portion must be able to be detected by the temperature detection means. In the case of the temperature detection means which uses roughly a radius segment of the mounting table at a particular location as its angle of view, if the positions of the power feed portion and the temperature detection means are not appropriate, the temperature of the object cannot be detected.
Further, one of the apparatus disclosed in the Japanese Patent Application Publication No. Hei9-27389 basically performs heating by rotating the mounting table to heat the objects evenly and, when temperature variations occur, the heating mode is switched to a concentrated heating or distributed heating to eliminate the temperature variations. Another apparatus basically performs heating by moving the power feed portion, rather than rotating the mounting table, to heat the objects evenly and, when temperature variations occur, the apparatus switches the power feed portion to the central or peripheral one to effect the concentrated heating and thereby eliminate the temperature variations. With these conventional apparatus, however, the power feed portion is moved and rotated and a waveguide 24 and power feed portions 20a, 20b are located at positions directly connected to a high-frequency generation means 25 where the electric field intensity is very strong. Moving the waveguide 24 and power feed portions formed of a metal (they are difficult to fabricate using materials other than metals) at positions exposed to a strong electric field will easily result in such phenomena as heating and spark due to electric field concentrations. Hence, the practical use of this arrangement is very difficult to realize.
Further, when a plurality of objects with different heat absorbing capacities, such as milk in a large cup and milk in a small cup, are to be heated simultaneously by the conventional apparatus of these arrangements, it is likewise not possible to simultaneously heat a plurality of objects to the same temperatures.
The present invention has been accomplished to solve the problems described above and provide a high-frequency heating apparatus and a heating method which can eliminate the necessity of moving and rotating the power feed portion and which can not only heat a single object to an appropriate temperature but also simultaneously heat a plurality of objects in different states having different temperatures at the start of heating and/or different heat absorbing capacities to the same temperatures.
To realize these, it is another object to provide a detailed arrangement that forms variations in a high-frequency radiation intensity in the heating chamber and also a means for taking advantage of this arrangement.
It is still another object to optimize a temperature detection means detection position for an area formed in the heating chamber near the power feed portion where the high-frequency radiation is strong.
When heating a particular object concentratedly with a high-frequency radiation, it is a further object to occasionally detect the temperatures of objects other than the particular object to select a lower-temperature object at all times and heat it concentratedly, thereby heating a plurality of objects to almost the same temperatures.
To solve the problems described above, the high-frequency heating apparatus of this invention positively forms variations in high-frequency radiation intensity in the heating chamber by the radiation variation means, puts a lower-temperature object or a lower-temperature part of the object at a position where the radiation is strong, and heat it while monitoring the surface temperature of the object by an infrared sensor, the temperature detection means.
With this invention, by strongly heating the lower-temperature object among a plurality of different kinds of objects or a lower-temperature part of the object while monitoring the surface temperature of the object, it is possible to eliminate the insufficient heating of one object relative to other objects.
Further, the high-frequency heating apparatus comprises: a power feed portion to supply a high-frequency power to a heating chamber; a mounting table to mount a plurality of objects to be heated thereon and apply more of the high-frequency power to the object located near the power feed portion than to objects located elsewhere; a temperature detection means to detect temperatures of the plurality of objects when the mounting table is rotating and, when the mounting table is stopped, monitor a temperature change of at least the object near the power feed portion; a decision means to determine a temperature difference between the objects being heated based on a detection result obtained from the temperature detection means when the mounting table is rotating; and a control means to stop the rotation of the mounting table when the lower-temperature object comes near the power feed portion according to a decision made by the decision means and to heat the object concentratedly and at the same time occasionally rotate the mounting table to check for a possible change of the lower-temperature object.
Further, when a plurality of objects are heated simultaneously, at least at some point during the heating operation, a lowest-temperature object is heated at a position where a high-frequency radiation is strongest in order to eliminate temperature differences among the objects being heated.
With this invention, the high-frequency heating by rotating the mounting table and the concentrated high-frequency heating of a particular object by stopping the mounting table can be combined, making it possible to simultaneously heat a plurality of objects having different temperatures at the start of heating and/or different heat absorbing capacities to the same temperatures, which has not been possible with the conventional high-frequency heating apparatus. This is very convenient. Further, because the power feed portion is not varied, phenomena such as heating and spark due to electric field concentrations do not occur and the apparatus can be realized with a simple construction. Further, a variety of choices is available according to the needs of the overall arrangement. For example, possible choices include a low-cost type, a simple structure type and intermediate type.